Industrial robots are known from U.S. Pat. No. 4,708,580 having a wrist axis which has three degrees of freedom, where the wrist axis has an internal conduit for signal and power lines. When the wrist axis moves in the individual degrees of freedom, the lines in the internal conduit of the wrist axis are either stretched or compressed in the axial direction and additionally subjected to torsional loading. This is compensated for in the known industrial robots incorporating a wrist axis of this kind by routing the lines in the internal conduit loosely and consequently providing adequate axial play.
The disadvantage of these known wrist axes is the fact that the lines can be damaged in operation because they are exposed to severe friction from the inner walls and the transitional radii in the internal conduit of the wrist axis. Such damage to the lines with industrial robots during production leads to costly stoppages. Furthermore, a complete bundle of lines has to be replaced if there is damage to one line, resulting in substantial repair costs.
A further disadvantage of the known wrist axes is that the lines in the internal conduit of the wrist axis are carried without suitable sealing in order to allow the wrist axis to move. As a result of the inadequate sealing of the lines, there can be an exchange of fluid between the wrist axis and the robot arm, requiring cost-intensive cleaning.